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UCC256304: L(N) in UCC25630x Design Calculator

Zhun Liu
Intellectual 290 points
Part Number: UCC256304


In UCC25630x Design Calculator,  Ln and Qe(Line 56 and 57)is 13.5. The default values are 13.5 and 0.15.

Could you tell me the meaning and function of Ln?

And if  I set it to 2~10,is it OK?  And what will happened about the performance of the circuit?

  • 0
    TI__Mastermind 27145 points
    Hi Zhun,

    Ln is the ratio between the magnetizing inductance and resonant inductance. you want to make sure that the Ln and Qe values you select for the power stage give you enough gain to deliver full load power.

    In the calculator, the blue curve represents the resulting gain curve for your selected Ln and Qe. You will want to make sure whatever values you select for the Ln and Qe results in at least a portion of the gain curve that is above the orange line, Mg(max).

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Intellectual 290 points
    Thank you.
    Just let the gain curve that be above the orange line is OK?
    It seems that if Ln is too low, the gain curve will be lower.
    If Ln is too high, what will happen?
  • 0 in reply to Zhun Liu
    TI__Mastermind 27145 points
    Hi Zhun,

    Typically higher gain in the LLC power stage requires higher circulating current which will reduce your efficiency. Typically you want enough gain in the power stage to maintain regulation across your operating range but not too much gain to where your efficiency suffers.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Intellectual 290 points
    Thank you very much.
    If I have a model that input is 220V AC, output is 19V8A ,
    could you indicate me the approximate range of value for Ln in this case ?
  • 0 in reply to Zhun Liu
    TI__Mastermind 27145 points

    Hi Zhun,

    Normally, a good place to start is Ln = 5 to 10 and Qe ~ 0.25 and iterate from there to obtain the desired gain and operating frequency range. This is more of a guideline rather than a hard limit and doesn't mean Ln and Qe values outside this range are incorrect however.

    Best Regards,

    Ben Lough